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Sauropod dinosaur embryos from the Late Cretaceous of Patagonia

Abstract

Definitive non-avian dinosaur embryos, those contained inside fossil eggs, are rare1,2. Here we describe the first known unequivocal embryonic remains of sauropod dinosaurs—the only known non-avian dinosaur embryos from Gondwana—from a nesting ground in the Upper Cretaceous stage of Patagonia, Argentina. At this new site, Auca Mahuevo (Fig. 1), thousands of eggs are distributed over an area greater than 1 km2. The proportion of eggs containing embryonic remains is high: over a dozen in situ eggs and nearly 40 egg fragments encasing embryonic material were recovered. In addition to bone, these specimens contain large patches of fossil skin casts, the first definitive portions of integument ever reported for a non-avian dinosaur embryo. As morphology of the eggs enclosing these osseous and integumentary remains is identical, we propose that these specimens belong to the same sauropod species. This discovery allows the confident association of the megaloolithid type of dinosaur eggshell3 with sauropod dinosaurs.

The eggs and embryos were collected from the Anacleto Member of the Río Colorado Formation. Previous age assignments for the fossils from the Río Colorado Formation have ranged from Coniacian to Campanian30, a wide geochronological interval extending from about 89 Myr to about 71 Myr. The eggs and embryos are restricted to a 5-m-thick interval of silty, pale reddish-brown mudstone stratigraphically located just below the midpoint of a 25-m-thick sequence of siltstones and fine- to medium-grained sandstone. These sediments seem to represent shallow palaeochannel and associated overbank deposits laid down on a low-gradient floodplain. The eggs and embryos are preserved exclusively in the finer-grained, overbank silts and muds.

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Figure 2: Bone morphology of the sauropod embryos from Auca Mahuevo.
Figure 3: Natural cast of the integument of the sauropod embryos from Auca Mahuevo.
Figure 4: Eggshell morphology of the Auca Mahuevo embryos.

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Acknowledgements

We thank J. Clarke, O. DiIorio, J. Guevara, N. Klaiseburd, C. Mehling, P. Puerta, S. Salvidia, and S. Zetkus for field assistance; J. McIntosh, J. Gauthier, and E. Buffetaut for comments and reviews; A. Klaus for the SEMs; L. Meeker for the photographs; and S. Orell for illustrations and editing. This work was supported by the National Geographic Society, the InfoQuest Foundation, the Image & Chemical Analysis Lab (ICAL, MSU), the F. Chapman Fund (AMNH) and the Dirección de Cultura (Gobernación de la Provincia del Neuquén, Argentina).

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Correspondence to Luis M. Chiappe.

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Chiappe, L., Coria, R., Dingus, L. et al. Sauropod dinosaur embryos from the Late Cretaceous of Patagonia. Nature 396, 258–261 (1998). https://doi.org/10.1038/24370

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